An object of size 7 cm is placed at 27 cm infront of a concave mirror of focal length 18 cm. At what distance from the mirror should a screen be placed to obtain a sharp image ? Find size and nature of the image.
Given that ${ H }_{ o }$ = 7 cm ; u = -27 cm ; f = -18 cm ; v = ?
The mirror formula is 1/f = 1/v + 1/u = 1/-18= 1/-27+ 1/v
1/v = -1/18 + 1/27
1/v = 3-2/ 54 = 1/54
So, v = 54cm
So the screen should be placed 54 cm from the mirror and the image is real and inverted.
Magnification,m = hi /ho = -v/u = hi/7 = -54/27 = hi = -54/27 x 7 = -14cm
So the image is enlarged two ti